Various blow-molding systems of the type in question are known, particularly systems equipped with various types of nozzles either designed to be brought into physical contact with the neck of the parison that is to be blow-molded (nozzles butting in a sealed fashion against the mouth of the neck of the parison, conical nozzles engaged in sealed fashion inside the neck of the parison, nozzles fitted tightly over the neck of the parison), or designed such that they are oversized relative to the neck of the parison so as to be brought to bear frontally and in a sealed manner against the wall of the mold supporting the parison while surrounding said neck from a distance (bell-shaped nozzles: see, for example, document FR 2 764 544).
The force with which the nozzle, whatever its type, is held bearing in a sealed fashion against the neck of the parison or against the wall of the mold has to be high enough to oppose the reaction thrust, in the opposite direction, due to the high pressure (typically of the order of 40×105 Pa) of the blow-molding fluid which is exerted on the walls of the nozzle. This bearing force has also to be high enough to seal the cooperation between the nozzle and the neck of the parison by slight elastic deformation of the thermo-plastic material and, in the case of the bell-shaped nozzle, for the seal provided transversely across the nozzle to be compressed enough that it is not driven radially off its seating under the effect of the high blowing pressure.
In practice, the movable equipment incorporating the nozzle is moved and kept bearing in a sealed fashion against the neck of the parison or the wall of the mold using a pneumatic actuator operated by a fluid under high pressure at least equal to the pressure of the blow-molding fluid, and the fluid delivered to the pneumatic actuator is the blow-molding fluid itself.
Now, from a financial standpoint, producing fluid at high pressure, typically at pressures of 40×105 Pa, represents a very significant item of expenditure in the operation of the entire thermoplastic receptacle (particularly bottle) production line: specifically, the higher the consumption of high-pressure fluid, the more highly specified the compressor needs to be, and therefore the more expensive it is, and furthermore, the higher its electrical power consumption.
Users are nowadays looking for manufacturing systems of improved profitability with higher production rates and lower operating costs. In this context, reducing the amount of high-pressure fluid used by the receptacle manufacturing line and, more particularly, by the blow-molding system, would seem to be desirable.